1. Field of the invention
The present invention is generally concerned with boxes sometimes called prefabrication boxes which, during the construction of an external or an internal wall, are fitted to the corresponding sheeting or shuttering before the concrete is cast so as to provide in the latter the necessary space for accommodating an equipment, for example an electrical equipment such as an electrical socket outlet or switch to be built into the wall.
It is more particularly directed to the situation where, for the purpose of connecting to the box a conduit to accommodate electrical conductors connected to the equipment concerned, there is provided on the side wall or on the back of the box an inlet providing access from the conduit to its interior space.
In practise a plurality of such inlets are provided so that the installer can choose which is the most suitable for the specific orientation of the conduit to be installed.
To prevent the box filling up when the concrete is cast any unused inlets have to be covered.
This therefore applies systematically to all inlets on a box as manufactured.
To remove the cover from the inlet that is to be used it is possible to cut it away using a special machine or a knife.
However, use of a special machine presupposes its presence on the worksite.
Cutting with a knife may cause damage if the operation is not done properly.
It has also been proposed to use knock-out covers, each being delimited by a line of reduced strength.
At present any such knock-out is removed by pushing it in or out.
As with cutting by means of a knife, this operation may cause damage if it is not carried out properly.
A general object of the present invention is an arrangement whereby it is possible to avoid such damage.